Disposable absorbent articles are well known in the art and have been commercially available for many years. Typically, a disposable article comprises a liquid pervious topsheet, a liquid impervious backsheet joined with the topsheet, and an absorbent core between the topsheet and the backsheet. The backsheet typically comprises a liquid impermeable material. Furthermore, the backsheet must be thin and flexible for comfort.
A long-felt need has existed for more convenient and discreet disposal methods for such absorbent articles, particularly for sanitary napkins and the like. One method that would provide such improved convenience and discretion is the use of a conventional toilet for such disposal. The core is easily made flushable. Likewise, a topsheet which does not comprise a formed film can be made flushable. Because the backsheet is liquid impermeable, there is a substantial risk of disposal problems, such as clogging, if commercially available sanitary napkins and similar disposable absorbent articles are disposed of by flushing down a conventional toilet. One way of resolving this problem is to provide a backsheet that would be both liquid impermeable and flushable.
A number of attempts have been made to provide flushable absorbent articles with flushable backsheets.
For example, British Patent No. 282,447 attempts a partial solution by providing a core said to be flushable and a repellent treated barrier which is separated from the core and needs to be disposed of by other means. U.S. Pat. No. 3,078,849, issued to Morse on Feb. 26, 1962, describes a sanitary napkin incorporating a fluid sensitive, temporary barrier within the absorbent core for spreading bodily fluids but makes no provision for a water sensitive outer coveting. U.S. Pat. No. 3,561,447, issued to Alexander on Mar. 13, 1969, describes a sanitary napkin having a nonwoven fabric covering wherein the nonwoven fabric comprises textile length fibers and a binder for the nonwoven having a combination of a soft acrylic binder and polyvinyl alcohol. This combination is said to have sufficient strength when damp to serve as an outer covering while still dispersing in water under mild agitation. While such a structure may have wet strength, it is unlikely that it will have sufficient barrier properties to be a satisfactory backsheet for a modem sanitary napkin. U.S. Pat. No. 3,665,923, issued to Champaigne, Jr. on May 30, 1972, describes a sanitary napkin with a wrapper comprising a nonwoven fiber web that is bonded by a water dispersible adhesive such as polyvinyl alcohol. A preferred embodiment also comprises a baffle member of a thin impervious plastic film interposed between the absorbent pad and the wrapper. This structure solves the problem of providing barrier properties by providing a non-dispersible member with the requisite barrier properties. Repeated flushing of such structures poses the risk of clogging sewer pipes because the baffle member will not disperse into small particles. U.S. Pat. No. 5,300,358, issued to Evers on Apr. 5, 1994 describes the absorbent structures wherein the backsheet comprises two sheets of polyvinyl alcohol film with a highly absorbent paper structure therebetween. All surfaces that may be exposed to aqueous fluids are treated with a water repellent material, such as a fluorocarbon. The absorbent structure is also provided with a tear strip or string which, when pulled at disposal, is said to expose the highly absorbent paper structure to water which then wicks the water to the non-repellent treated surfaces so they can dissolve. The requirement of a tear strip is an obvious inconvenience.
One particular attempt to resolve the problem has been to use a backsheet having a flushable substrate coated with a substrate having the necessary barrier properties and being compostable when flushed. An example of such an attempt is illustrated in commonly assigned U.S. Pat. No. 5,417,679, issued May 23, 1995 to Toms et al., which patent is incorporated herein by reference.
U.S. Pat. No. 5,116,563, issued to Dennis A. Thomas et al, on May 26, 1992, describes a process not having matched velocities, but useful for forming mechanical fastening prongs by depositing a heated resinous material onto a substrate. The substrate is transported at a speed from approximately 25% greater than to approximately 15% less than the speed of a roll depositing the resinous material. This process, however, does not produce a thin, uniform and flexible coating of a resin on a substrate.
Thus, it is an object of the present invention to provide a process for producing a uniform, thin and flexible web that is liquid impermeable and yet water dispersible, and which can be used in flushable disposable absorbent articles. It is a further object of the present invention to provide a process for producing a uniform, thin and flexible web that readily disperses into small portions when exposed to water and thereby is disposable by flushing a conventional toilet. It is still another object of the present invention to provide a process for producing a liquid impermeable web from a water permeable substrate, said impermeable web having a greater tensile strength than the substrate, without increasing the caliper of the substrate.